Ultra-coarse grained tungsten powder was prepared by high-temperature hydrogen reduction without additives,and the reduction process and the quality of tungsten powder were analyzed to discuss the influence of process conditions on the quality of tungsten powder.The tungsten powder and carbon black were uniformly mixed,pressed and then carbonized at 2100℃and 2300℃,respectively.The microstructure of tungsten carbide obtained at different temperatures was compared.The results show that the tungsten powder with an average particle size of more than 30μm,uniform particle size and low agglomeration could be produced under the conditions of above 1300℃and high water vapor partial pressure.Carbonization at a relatively high temperature could produce ultra-coarse grained tungsten carbide powder with single composition,good wear resistance and few defects.The cemented carbide prepared with the tungsten carbide obtained at 2300℃has an average grain size of 8.1μm,and it has higher flexural strength and impact wear resistance than the cemented carbide prepared with the tungsten carbide obtained at 2100℃.

Ultrafine WC-8Co and WC-6Co cemented carbides strengthened by composite carbides were prepared by vacuum sintering and low pressure sintering,respectively.The effects of sintering method and sintering temperature on the properties and microstructure of the cemented carbides were studied.The results show that compared with vacuum sintered cemented carbide,low pressure sintered cemented carbide has fewer pores with higher density,hardness and bending strength.With the increase of low pressure sintering temperature,all the density,hardness and flexure strength of the cemented carbide increase.However,excessively high temperature during low pressure sintering could lead to abnormal growth of WC grains.

WC-12Co cemented carbide was formed by selective laser melting using two protective gases of nitrogen and argon.The phase composition,microstructure,element distribution and hardness of the formed WC-12Co cemented carbide were analyzed by X-ray diffractometer,scanning electron microscopeenergy dispersive spectrometer and Rockwell hardness tester.The results show that compared with nitrogen as the protective gas,WC-12Co cemented carbide formed in argon has the advantages of few pores,small grain size and high hardness.It provides a reference for the selection of protective gas for subsequent selective laser melting forming of WC-12Co cemented carbide.

Taking nickel-based powder superalloys for turbine disks as the research object,gradient change of γ′microstructure morphology and size was achieved on a single sample by gradient cooling.The effect of solid solution cooling rate on the microstructure and mechanical properties of the alloy was investigated by scanning electron microscope observation and Vickers hardness test.The effect of solid solution cooling rate on the element segregation behavior in γ phase and γ′phase was investigated by three-dimensional atomic probe analysis.The results show that with the decrease of solid solution cooling rate,the size of γ′phase gradually increases and then tends to be stable.The size ofγ′phase is smaller and the shape is nearly spherical at a faster solid solution cooling rate.At a slower solid solution cooling rate,the γ′phase is distributed in the form of secondary γ′phase and tertiary γ′phase,and the size of the secondary γ′phase is larger.Different solid solution cooling rates have no obvious effect on the element distribution in γ phase and γ′phase.Ni,Al,Ti and Nb are mainly distributed in the γ′phase,while Co,Cr and Mo are mainly distributed in the γ matrix phase,and no obvious segregation of W element is observed.Due to the use of the gradient cooling experimental method,the range of cooling rate is too large,and multiple inflection points of hardness change are captured in the experimental results.The alloy hardness shows a nonlinear change trend with the decrease of solid solution cooling rate.

The preparation of high purity ammonium paratungstate not only has important economic value,but also has great strategic significance.Reasonable control of molybdenum content in ammonium paratungstate and guarantee of product pass rate are the key to affect the development and economic benefits of enterprises.The effects of washing water pH value,washing temperature,washing time,liquid-solid ratio and washing frequency on the elution rates of molybdenum and tungsten were studied by single factor tests.The results show that the optimal conditions for molybdenum reduction from ammonium paratungstate by washing with pure water are washing water pH value of 7.0,reaction time of 20 min,reaction temperature of 65℃,liquid-solid ratio of 3∶1 and washing frequency of once.At this time,the elution rate of molybdenum reaches 82.01%,and the loss of tungsten is small with an elution rate of 3.97%.This method has the advantages of no other impurities,simple operation,environmentally friendly process and low production cost,and has certain reference value and significance for enterprise development and process improvement of ammonium paratungstate preparation.

The response surface method was used to investigate the molybdic acid precipitation process by adding sulfuric acid in the ammonium molybdate solution system,as the existing process suffers from low raw material utilization and poor quality and non-uniform particle size of the product.A optimizated quadratic polynomial regression model was established for the three process parameters of acid precipitation temperature A,initial MoO₃ concentration B,and end pH value of acid precipitation C and their interactions,with the molybdenum direct yield Y as the response value.Based on the one-factor experiments,the optimized regression model was obtained as Y=-125.19+5.96A+0.30B-9.80C+4.63×10^-4AB+0.92AC-0.07BC-0.048A²-1.87×10^-3B²-24.80C².The experimental results reveal that the molybdic acid precipitation process is controlled by multiple factors and sensitive to the response of individual factors with significant interactions.The order of influence significance of single factor is C>A>B,and the order of influence significance of interaction is AC>BC>AB.The optimized acid precipitation conditions are as follows:a stirring intensity of 450 r/min,a acid precipitation temperature of 72℃,an initial MoO₃ concentration of 70 g/L,an end pH value of 1.09 controlled by the back-addition method,and a heat preservation time of 180 min.Under the above conditions,the average molybdenum direct yield of 94.53%is achieved with a relative standard deviation of only 0.44%.The obtained molybdic acid is of high purity,good morphology,and relatively uniform particle size.

A optimal production practice study was conducted to address the issues of outdated equipment,high production costs and poor product quality consistency in the pilot production line of PrNd metal prepared by molten salt electrolysis method in a certain company.The results from the production practice show that by upgrading high-frequency switch power supply,modifying electrolytic wires,optimizing the design of electrolytic cells and controlling the quality of raw materials and product carbon content,the output of each furnace increases by 5.6%,the unit consumption decreases by 0.28%,the electricity consumption decreases by 18.6%,the first pass rate increases from 85%to 95%,and the consistency of product quality improves after optimization and upgrade.The optimal production practice can achieve the goal of reducing electri-city consumption and unit consumption and solving the problem of poor product quality consistency.

The process and reaction principle of lithium extraction from lepidolite were analyzed.Thermodynamic calculation,energy consumption comparison and phase diagram analysis were carried out for the two key steps of lithium extraction process from lepidolite,namely roasting energy saving and hydrometallurgical salt precipitation.The results show that the energy consumption of ordinary tunnel kilns is slightly lower than that of ordinary rotary kilns.Considering both investment and heat exchange efficiency,hot air combustion-assisted rotary kiln process with grate cooler is the best sulfate roasting process for lithium extraction from lepidolite.Pure mirabilite can be obtained by crystallization of purified leaching solution at 0℃.Na₂SO₄·3K₂SO₄ double salt can be obtained by evaporation crystallization at 15~50℃,and the precipitated Na₂SO₄·3K₂SO₄ at 25℃is the most.Only lithium-containing mixed salt can be obtained by evaporation crystallization at 100℃.

The thermodynamic calculation and simulation of direct carbothermal reduction of germanium dioxide for preparation of germanium metal and the verification experiments were carried out to explore the feasibility of short process preparation of germanium metal.Firstly,the standard Gibbs free energy change of each reaction in GeO₂-C and GeO₂-C-O₂ systems was calculated.Secondly,the multiphase simultaneous equilibrium of the two systems was simulated.Finally,the reduction experiment was carried out with pure germanium dioxide and carbon powder as raw materials in an inert atmosphere at 900℃.The results show that in the inert atmosphere,the increase of temperature is conducive to the carbothermal reduction of GeO₂ to produce GeO and Ge,and more carbon result in greater Ge yield.In the oxygen atmosphere,carbothermal reduction products of CeO₂ include GeO and Ge.However,oxygen preferentially reacts with carbon to produce CO₂,which is not conducive to the control of GeO₂ reduction process.The product of the reduction experiment is pure germanium metal with a direct recovery rate of 87.56%,which proves the feasibility of direct carbothermic reduction of germanium dioxide to prepare germanium metal.

GCr15 bearing steel with rare earth Y was prepared by vacuum arc melting method,and then heat treated with different process parameters.The phase,microstructure,Vickers hardness and frictional wear properties of the samples were characterized by X-ray diffractometer(XRD),scanning electron microscope(SEM),micro Vickers hardness tester and frictional wear tester.The results show that compared with GCr15 steel without rare earth Y,GCr15 steel with 0.036%Y has smaller grain size,greater lattice distortion,and more uniform carbide distribution.When the quenching temperature and holding time is 830℃and 20 min,and the tempering temperature and holding time is 160℃and 30 min,the GCr15-Y steel has the highest hardness of 814 HV and the smallest friction coefficient of 0.158.At this time,the furrow is shallow and narrow,the wear is the lightest,and the wear resistance is the best.The wear mechanism of GCr15-Y bearing steel under dry friction condition is mainly abrasive wear and adhesive wear.